13- COMPUTER VIRUS

A computer virus, much like a flu virus, is designed to spread from host to host and has the ability to replicate itself. Similarly, in the same way that flu viruses cannot reproduce without a host cell, computer viruses cannot reproduce and spread without programming such as a file or document.

In more technical terms, a computer virus is a type of malicious code or program written to alter the way a computer operates and is designed to spread from one computer to another. A virus operates by inserting or attaching itself to a legitimate program or document that supports macros in order to execute its code. In the process, a virus has the potential to cause unexpected or damaging effects, such as harming the system software by corrupting or destroying data etc.

A computer virus is a type of malicious software program "malware" that, when executed, replicates by reproducing itself (copying its own source code) or infecting other computer programs by modifying them. Infecting computer programs can include as well, data files, or the "boot" sector of the hard drive. When this replication succeeds, the affected areas are then said to be "infected" with a computer virus. The term "virus" is also commonly, but erroneously, used to refer to other types of malware. "Malware" encompasses computer viruses along with many other forms of malicious software, such as computer "worms", ransomware, trojan horses, keyloggers, rootkits, spyware, adware etc.

Viruses often perform some type of harmful activity on infected host computers, such as acquisition of hard disk space or central processing unit (CPU) time, accessing private information (e.g. credit card numbers), corrupting data, displaying political or humorous messages on the user's screen, spamming their e-mail contacts, logging their keystrokes, or even rendering the computer useless. However, not all viruses carry a destructive "payload" or attempt to hide themselves—the defining characteristic of viruses is that they are self-replicating computer programs which install themselves without user consent.

Once a virus has successfully attached to a program, file, or document, the virus will lie dormant until circumstances cause the computer or device to execute its code. In order for a virus to infect your computer, you have to run the infected program, which in turn causes the virus code to be executed.

An article that describes "useful virus functionalities" was published by J. B. Gunn under the title "Use of virus functions to provide a virtual APL interpreter under user control" in 1984. The first IBM PC virus in the "wild" was a boot sector virus dubbed (c)Brain, created in 1986 by Amjad Farooq Alvi and Basit Farooq Alvi in Lahore, Pakistan, reportedly to deter unauthorized copying of the software they had written. The first virus to specifically target Microsoft Windows, WinVir was discovered in April 1992, two years after the release of Windows 3.0. The virus did not contain any Windows API calls, instead relying on DOS interrupts. A few years later, in February 1996, Australian hackers from the virus-writing crew VLAD created the Bizatch virus (also known as "Boza" virus), which was the first known virus to target Windows 95. In late 1997 the encrypted, memory-resident stealth virus Win32.Cabanas was released—the first known virus that targeted Windows NT (it was also able to infect Windows 3.0 and Windows 9x hosts).

Even home computers were affected by viruses. The first one to appear on the Commodore Amiga was a boot sector virus called SCA virus, which was detected in November 1987.

There are three types of computer virus given below:

1- Boot Sector Virus

2- File Virus

3- Other Virus

1- Book Sector Virus:

A boot sector or boot block is a region of a hard disk, floppy disk, optical disc, or other data storage device that contains machine code to be loaded into random-access memory (RAM) by a computer system's built-in firmware. The purpose of a boot sector is to allow the boot process of a computer to load a program (usually, but not necessarily, an operating system) stored on the same storage device. The location and size of the boot sector (perhaps corresponding to a logical disk sector) is specified by the design of the computing platform. On an IBM PC compatible machine, the BIOS selects a boot device, then copies the first sector from the device (which may be a MBR, VBR or any executable code), into physical memory at memory address 0x7C00. On other systems, the process may be quite different.

2- File Virus:

A file-infecting virus is a type of malware that infects executable files with the intent to cause permanent damage or make them unusable. A file-infecting virus overwrites code or inserts infected code into a executable file like .exe and  .com extension.

3- Other Virus:

A computer virus is a type of malicious software program ("malware") that, when executed, replicates by reproducing itself (copying its own source code) or infecting other computer programs by modifying them. Infecting computer programs can include as well as data files (documents, accounting, inventory stock files)  that making by other programs.

How to Prevent Computer Virus Infection:

There are many tips prevent the virus infection in computer. Some are below:

a- Don't open unknown attachments in emails. 

b- Don't open without scans file to secondary storage device as well as

     micro SD or Mini SD, Pen Drive etc.

c- Downloads the files only from trusted sites.

d- Remember to do a virus scan for them after peripheral devices are 

     connected to your computer.

e- Always use a registered anti virus program to prevent the virus 

     protection.

Use Trusted Anti Virus Sortware:

Anti virus or anti-virus software (often abbreviated as AV), sometimes known as anti-malware software, is computer software used to prevent, detect and remove malicious software. There are some popular anti virus software that prevent the virus infection to you computer-

i- Norton Anti Virus viii- Guardian Anti Virus

ii- MCAfee Anti Virus ix- Kesper Sky Ati Virus

iii- AVG Anti Virus         x- ESet Anti Virus

iv- Quick Heal Anti Virus xi- Avira Anti Virus

v- Norman Anti Virus xii- Avast Anti Virus

vi- Defender Anti Virus xiii- Trand Macro Anti Virus

vii- Net Protector Anti Virus (NP AV) xiv- BullGuard Anti Virus